The present invention relates to an ink jet print head of a type in which piezoelectric conversion elements are selectively driven thereby to eject ink interposed between the piezoelectric conversion elements and a nozzle plate onto a recording medium from nozzles provided in correspondence to the piezoelectric conversion element in the form of ink droplets.
Japanese Patent Examined Publication No. 8953/1985 discloses ink jet printers of a type in which a plurality of piezoelectric conversion elements immersed in an ink droplet are selectively driven to pressurize and eject the ink droplet present in a nozzle gap formed between the conversion members and a nozzle plate to record an image on a recording medium. This type of printer, which requires neither an ink pressurizing chamber nor an ink flow path, not only allows the print head to be formed in a very small structure but also contributes to greatly reducing power consumption for printing by its efficient operation of ejecting the ink in the form of droplets, which is achieved by making the nozzle gap as small as possible. In addition, the use of a hot melt ink which can be converted into a liquid phase when heated permits the printing of images free from bleeding.
However, the print head used in this type of printer uses piezoelectric conversion elements, each composed of a lamination of a piezoelectric plate and a metal plate. These piezoelectric conversion elements are susceptible to temperature-dependent, bimetal-like deformation due to a difference between the linear expansion coefficients of their materials. For this reason, when the base of each piezoelectric conversion element is fixed on the nozzle plate by an adhesive that has been rendered molten by heating during the assembly process, each piezoelectric conversion element is deformed noticeably due to the accompanying heating, causing variations in nozzle gap between the nozzle plate and the conversion member even after cooling to ambient temperature. Since this nozzle gap affects the ink ejecting characteristics, the assembly process thus causes variations in nozzle gap among the individual piezoelectric conversion elements, which is of course a problem in this type of print head In addition, the piezoelectric conversion elements of even those printers using an ordinary liquid ink are likewise subjected to deformation at their normal operating temperature range between 0.degree. and 40.degree. C., thereby presenting the problem of impairing the quality of images recorded due to the temperature-dependent ink jetting characteristics.